.nav-belt{
    height: 60px;
    background-color: green;
}


.nav-left{
    width: 200px;
    height: 60px;
    background-color: yellow;
    float: left;
}

.nav-middle{
    height: 60px;
    width: 1000px;
    background-color: red;
    float: left;
}
.nav-right{
    height: 60px;
    width: 336px;
    background-color: blue;
    float: right;
}